#include <vector>
class Solution
{
    int m, n;
    int vis[1001][1001] = { 0 };
    int dx[4] = { 0, 0, 1, -1 }, dy[4] = { 1, -1, 0, 0 };
public:
    int rotApple(vector<vector<int> >& grid)
    {
        m = grid.size(), n = grid[0].size();
        queue<pair<int, int>> q;
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                if (grid[i][j] == 2)
                    q.push({ i, j });
        int ret = 0;
        while (q.size())
        {
            int sz = q.size();
            ret++;
            while (sz--)
            {
                auto [a, b] = q.front();
                q.pop();
                for (int k = 0; k < 4; k++)
                {
                    int x = dx[k] + a, y = dy[k] + b;
                    if (x >= 0 && y >= 0 && x < m && y < n && !vis[x][y] && grid[x][y] == 1)
                    {
                        vis[x][y] = true;
                        q.push({ x, y });
                    }
                }
            }
        }

        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (grid[i][j] == 1 && !vis[i][j])
                    return -1;
            }
        }
        return ret - 1;
    }
};